Make the dough. Whisk the all-purpose flour, rye flour, cornmeal, caraway seeds, cocoa, salt, and instant yeast in a big bowl. Combine the water, olive oil, and molasses in a measuring cup or bowl. (Psst: If you measure the olive oil first, then the molasses, it'll slide right out of the spoon instead of sticking to everything.) Add the liquid ingredients to the dry and stir together with a wooden spoon or rubber spatula. It will yield a very sticky dough.,Cover the bowl with plastic wrap and let rise for about 1 hour, or until doubled in size.,When it's ready, preheat the oven to 425° F and arrange a rack in the lower third. Line a rimmed sheet tray with parchment.,Add 3 tablespoons olive oil to the sheet tray. Touch your palms to the oil, to grease them just a bit. Now deflate the focaccia dough by pulling the edges toward the center. Transfer to the sheet tray and roll around in the oil. Use your palms and fingertips to flatten into a rectangle. When it resists stretching any further, leave it alone. Let be for 20 minutes. Right before you bake, use your fingertips to flatten the focaccia a little more, so it fills out the pan.,______,When the focaccia has completely cooled, build the open-faced slab sandwich. Spread with Greek yogurt (an offset spatula works well here). Layer with lox. Sprinkle with onion, then capers, then dill. Cut into squares or rectangles.